Greater fuel efficiency and lower operating noise have traditionally been important objectives in the design of internal combustion engines, but the rising cost of fossil fuel and increasing concern over noise pollution has greatly intensified the need to achieve higher levels of performance in these areas. One fundamental approach for improving strength to weight ratio has been to provide specialized load bearing structure within the engine block to enable the engine block to better withstand concentrated loads without substantially increasing the overall weight of the block. For example, U.S. Pat. No. 3,046,952 to Dolza discloses a light weight engine block wherein elongated steel bolts extending through the block are each connected at one end to the engine head and at the other end to a respective main bearing cap. In addition to increased assembly and manufacturing costs, the use of such elongated bolts requires an overall increase in the size of the engine block by necessitating increased spacing between cylinder cavities. This increased spacing is required, in part, because the bolts are under tension at all times and the block must accordingly be strengthened in the vicinity of the bolts to withstand the bolt tension. One proposed solution to this problem illustrated in U.S. Pat. No. 4,059,085 to Mansfield et al has been to provide an internal combustion structure in which the cylinder head and main bearing caps are linked by a framework of members including pairs of tension members. While useful in some circumstances, the disclosed framework includes members angled obliquely to the direct line between head and caps which unduly enlarges the overall engine size.
A variety of composite engine block designs have also been proposed in attempts to optimize the often conflicting goals of high strength, low cost and compact size. For instance, U.S. Pat. No. 3,351,044 to Pomeroy discloses an internal combustion engine including an upper unit containing plural cylinder cavities and a lower unit containing a crankshaft to which the engine oil pan is attached on the lower side. While some advantages may be achieved with this design, such as facilitating engine assembly, no strength improving advantages are disclosed by the use of this composite design. The Pomeroy patent also discloses a pair of bolt-on water jackets for use on the respective sides of the upper unit thereby achieving a streamlined outer engine configuration and simplified coolant system. However, this patent fails to suggest any way in which the advantages of such a bolt on jacket can be used while simultaneously reducing the number of component parts and avoiding at least some of the increased seal leakage potential which naturally attends the use of two separate bolt on water jackets.
The use of cylinder liners in internal combustion engines has long been recognized as desirable as a means for improving internal combustion engine design and is especially desirable because it allows greatly simplified engine overhaul. One particularly desirable liner design is disclosed in British Pat. No. 615,045, accepted Dec. 31, 1948, wherein the liner is provided with an exterior stop positioned intermediate the ends of the liner for engagement with a liner stop located within the cylinder cavity at a substantial distance from the head engaging surface of the engine block. This design affords numerous advantages over liner designs employing a liner stop located at the top of the liner by allowing, for example, improved head gasket sealing during engine operation. The provision of mid stop liners, however, creates complications in routing the coolant and lubrication fluid flow passages through the engine without substantially increasing the size or complexity of the engine block design. U.S. Pat. No. 2,681,054 to Boghassian discloses an integral cast block for receiving mid stop cylinder liners wherein the camshaft and crankshaft bearing supports are cast integrally within the block. However, no portion of the space between the cylinder liners is utilized for the lubrication fluid return flow passage requiring other portions of the engine block to provide this function. Provision of an integral oil gallery within the disclosed engine block design of the Boghassian patent permits supply of lubrication fluid to both the crankshaft and camshaft bearing supports through passageways integral with the engine block but plural angularly arranged passageways are required for each set of interlinked crankshaft and camshaft bearing supports.
A great variety of engine block designs are known which employ cross walls extending between the cylinder cavities of the engine to provide support to the outer side walls of the engine block. One example of such a cross wall design is disclosed in U.S. Pat. No. 2,129,906 wherein a large aperture is provided in the cross wall as illustrated in the drawings of this patent. While such a cross wall design will reduce engine weight as compared with solid cross wall designs, there is no disclosure in this patent which would suggest how a cross wall design of the type illustrated could be used to provide sufficient strength to the liner stops within the engine block. In short, the prior art of engine block design is devoid of an optimum engine design which simultaneously provides high strength, low cost and compact size.